Recent advances in motor vehicle safety systems involve systems that deploy various safety systems differently depending on various crash-related parameters. Typical safety systems deployed include airbags, multistage airbags, side impact airbags, seat belt tensioners and the like. The growing capacity of modern safety systems allows variations in deployment responding to the severity of a crash, and the weight and position of the vehicle occupant. The growing safety system capabilities together with improvements in the engineering understanding of the crash environment, has led to tailoring the deployment decision to consider more than simply a threshold test. Particularly with multistage airbags, information about crash severity, and vehicle occupant type and position are being used to determine deployment timing and strategy.
Data from an acceleration sensor is typically verified by a mechanical crash sensor, then analyzed to determine crash severity and crash type. Empirically derived relationships between the magnitude of the accelerations measured and the rate of onset of acceleration are used together with vehicle-specific parameters to select a deployment strategy. In a severe crash the time available for analysis is very short, and the deployment decision must be made with only a limited amount of acceleration data. Although acceleration can be integrated to determine velocity, very little velocity is lost before most of the damage occurs. Thus by the time acceleration data gives an indication of crash velocity it is too late for effective deployment of safety systems.
Crash velocity is important data input because the energy of a moving system increases with the square of the velocity. Relatively small increases in crash velocity result in substantially more energy being dissipated by the crash. Ultimately, energy dissipated in a crash characterizes to a significant extent the severity of the crash. Systems to detect imminent crashes have been developed. For example U.S. Pat. No. 5,949,366 to Herrmann teaches a system using radar which can determine crash velocity and lateral offset of a crash.
What is needed is a method of combining velocity of impact with acceleration data, and with biomechanical parameters to develop a more optimal safety device deployment strategy.